1. Field of the Invention
The present invention relates to a bipyridine-based metal complex and an ink composition comprising the same, and more particularly, to a bipyridine-based metal complex in which metal is coordinated with bipyridine-based ligands having superior coloring ability and durability, and an ink composition comprising the complex as a coloring agent.
2. Description of the Related Art
In general, coloring agents embody their inherent colors by selectively absorbing or reflecting visible light, and are classified as dyestuffs and pigments.
Dyestuffs are used in any materials to be dyed, thus providing considerable fastness to daylight, washing, friction, and the like. Pigments are coloring matters in the form of particulates, and are not absorbed into the material to be dyed but adhere to the surface of the material to be dyed by physical means (e.g., adhesion, and the like), thus providing their inherent colors.
Dyestuffs are used as coloring agents in fibers, leathers, furs, papers, foodstuffs, t medicines, cosmetics, ink-jet inks, and the like, and pigments are used in paints, printing ink, plastics, rubber, furniture manufacturing, textiles, papers, cosmetics, ceramics, and the like.
The colors embodied by the coloring agents are determined by the wavelengths in the visible light range of 3,000 to 7,000 Å selectively reflected or transmitted by the particles of the coloring agent. The coloring agents may be classified into organic coloring agents and inorganic coloring agents based on their molecular structures. In the organic coloring agents, the colors are embodied by cycles of absorbing, transferring and transmitting light through conjugation of double bonds, and in the inorganic coloring agents, the colors are embodied by the ligands coordinated with metals in the compounds absorbing light, thus putting the ligand-metal complex in an excited energy state, and then emitting light by lowering to base energy level.
In general, organic coloring agents may embody a wide range of colors, and their colors are bright and clear, but they have problems of weak light resistance causing decoloration or discoloration. On the other hand, inorganic coloring agents are very durable and have good light resistance, but embody a narrow range of colors and have limited classes.
Various coloring agent compounds, for example, pigment complex compounds, employing metal complexes are disclosed in U.S. Pat. Nos. 3,971,739, 3,987,023, 4,077,953, 4,152,324, and Japanese Unexamined Patent Application No. 2001-152044. These patents disclose methods in which a metal is incorporated into an azo group containing compound to form a complex compound by forming covalent bonds using intramolecular coordinate bonds.
However, in such methods, the compounds should comprise a specific functional group of an azo group, and the compounds should comprise both a coordinate bond functional group and a covalent bond functional group within molecules such that coordinate bonds and covalent bonds are formed at proper distances when reacting with metal compounds. Also, the above disclosed complex compounds are not satisfactorily durable and cannot embody a wide range of colors, and the like. Thus, there remains a need for improvements in the compounds.